1. Field of the Invention
This invention relates to an apparatus for needling a web, comprising a deck, which is provided with a grate of parallel blades for supporting the web, at least one driven needle board for needling the web as it is conveyed over the deck, and a stripper plate, which has needle-receiving through holes and is disposed between the needle board and the grate of parallel blades.
2. Description of the Prior Art
When it is desired to needle a web, the needles of the needle boards are moved at a predetermined stroke frequency through the through holes of the stripper plate into the web, which is conveyed over the table. As the needles are pulled out, the stripper plate prevents a lifting of the web from the deck. The web support which is constituted by the deck must have suitable openings for receiving the points of the needles which have penetrated the web. For that purpose it is known to provide as a support for the web a perforated plate provided with holes in a spacing which is equal to the needle spacing. If loops for forming surface patterns are pulled adjacent to that surface of the web which faces the deck, the provision of a perforate plate as a web support will involve the risk that such loops may protrude into the holes for receiving the needle points and bulges may be formed in the web and such loops or bulges may considerably increase the resistance to the withdrawal of the web. For this reason, the perforate plates have been replaced by grates of parallel blades extending in the direction of travel of the web. But such grates of parallel blades have the disadvantage that the required strength of the blades will impose a restriction regarding the needle density in the direction which is transverse to the direction of travel of the web, particularly because the needles can be arranged only in longitudinal rows. On the other hand, the needle density and the distribution of the needles in a direction which is transverse to the direction of travel of the web will have an important influence on the result of the needling operation because the density of the points of penetration in a direction which is transverse to the direction of travel cannot be changed by a control of the speed of travel of the web whereas such control can be adopted to change the density of the points of penetration in the direction of travel. For that reason the spacing of the blades must be selected in close adaptation to the spacing of the rows of needles and an alteration of the needling apparatus to a different distribution of the needles will require a replacement not only of the needle board and stripper but also of the web-supporting grate of parallel bars.